There is near universal acceptance of the view that imitative processes play an important role in the early cognitive, social and personality development of the child. The role of imitation in linguistic development is also critical. Vocal imitation is the principal vehicle for infants' learning of their "mother tongue" -- the phonetic inventory and the prosodic structure of their native language. Experiments in the investigators' laboratories suggest that infants' abilities to imitate have been underestimated by traditional developmental theories. Infants can imitate facial gestures at birth, a skill that was postulated to appear first at about one year of age. Recent findings with older infants demonstrate imitation among infant peers, infant imitation from television, and the deferred imitation over delays as long as one week. New findings on vocal imitation indicate vowel imitation in 18-week-olds and suggest that the capacity for vocal imitation may exist as early as 12 weeks of age. Moreover, experiments with nonspeech sounds show that this early ability is quite selective; infants imitate speech sounds but fail to vocalize to nonspeech sounds that mimic certain properties of human speech. Studies are proposed investigating two different kinds of imitative acts, gestural and vocal, during the first two years of life. Although each of the domains has specific concerns guiding the design of the experiments, of interest are the issues that are common to both. Examples of these common concerns are: the origins and basis of infants' imitative abilities; the nature of the stimulus most effective in eliciting imitation; the effects of experience and development on imitation; and the functional significance and social utility of this behavior. The proposed research brings together expertise from two separate disciplines, developmental psychology and speech and hearing sciences.